In order to ensure for the oxidation-reduction reactions between the electrolyte and the electrode of a voltaic cell a large reaction surface, on the one hand, and to ensure also a transportation of electrolyte to the reaction surface, on the other hand, it has been proposed in U.S. Pat. No. 4,109,060 to make the electrode by sintering iron powder granules which have a high porosity, by which the desired large reaction surface is provided. Electrolyte can be transported through the coarse pores between the iron powder granules which have been sintered together. As a result, the electrochemical requirements can be met in that the sintered electrode has sufficient fine and coarse porosities in combination. To provide fine pores and coarse pores, the granules are made from an iron(III) oxide powder which has a particle size not in excess of 10 micrometers in order to permit the making of a sintered body having the desired coarse porosity. Said granules are optionally dried at a temperature between 600.degree. and 1200.degree. C. and are reduced at a temperature between 500.degree. and 800.degree. C. in order to ensure that each granule has the desired fine porosity and to effect a sintering which imparts to the iron powder granules the inherent strength which is required for the subsequent compacting of the reduced granules. The sinterable body which has been compacted under a pressure which is preferably between 250 and 500 kg/cm.sup.2 is sintered at a temperature between 600.degree. and 750.degree. C. under a protective gas atmosphere. But that known manufacturing process has the disadvantage that the production of the granules is rather expensive, particularly because a sufficiently large green strength is required, and that the reduced iron powder granules are destroyed as they are compacted so that sufficiently large coarse pores are not obtained in a sufficiently large number. Because large transport pores are present only in an insufficient number, only an inadequate transportation of electrolyte into the sintered electrode is enabled.